Meiosis I BIO 105 Cr.4
UW - L
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This 0 page Class Notes was uploaded by MaKena Betler on Monday November 9, 2015. The Class Notes belongs to BIO 105 Cr.4 at University of Wisconsin - La Crosse taught by a professor in Fall 2015. Since its upload, it has received 31 views. For similar materials see General Biology in Biology at University of Wisconsin - La Crosse.
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Date Created: 11/09/15
Lecture 25 Meiosiil Importance of meiosis 0 There are drawbacks to only reproducing asexually by mitosis o In order to maintain diversity a species needs to reproduce sexuaHy o Meiosis is needed in order to generate gametes that are haploid which can combine in fertilization to produce diploid progeny This greatly increases genetic diversity 0 One or more copies of an organism s genes are encoded on the chromosomes 0 Haploid has one set of chromosomes 1n2 o Haploid organisms only have a single copy a single allele of each gene 0 Diploid has two 39sets of chromosomes 2n4 o Diploid organisms have two copies alleles of each gene one from each set of chromosomes 0 The gene pool is the variety of alleles versions of genes present in the entire population 0 Regardless of the size of the gene pool an organism only has one allele haploid or two alleles diploid in its gene at any time Asexual reproduction by mitosis creates genetically identical progeny 0 An organism that has adapted to a stable environment over a long period will likely have the optimized gene alleles for that environment Genetically identical progeny might not be optimized for changing environment o If the environment changes a cell s progeny must adapt to that new environment using only the alleles present in their genome 0 An organism can acquire quotnew allelesquot by mutation this is a slow process 0 Coral reefs face extinctions due to rapid changes in ocean temperature and chemistry 0 Corals reproduce asexually and sexually sexual reproduction increases resilience in face of change 0 A sexual life cycle 0 3 stages of sexual life cycle Cell division mitosis Gamete production meiosis Gamete fusion fertilization Prophase l o Condensation of chromosomes 0 Synapsis o Crossing over 0 Prometaphase l o The rest of meiosis l Metaphase Anaphasel Telophase l Interkinesis no DNA replication between rst and second meiotic division 0 To prophase II in second meiotic division Meiosis II is same process but makes a total of four cells Fertilization haploidtodiploid and meiosis diploidtohaploid are reverse processes that each contribute to sexual mixing 0 Fertilization two haploid 1n cells fuse to make one diploid 2n cell with two copies of each chromosome 0 Meiosis one diploid 2n cell undergoes a nuclear division that produces four haploid 1n cells quot1 to quot4quot each haploid cell having a novel mixture of the chromosomes 0 During fertilization and meiosis chromosomes meet new versions of the other chromosomes and also exchange alleles crossing over with the homologous chromosomes they meet 0 Meiosis and fertilization bring about genetic variation Crossingover between homologous chromosomes Independent assortment of homologous chromosomes 2 combinations possible Humans 23 pairs of chromosomes 2238388608 combinations Random mating bringing genes from two parents together Sexual organisms mix alleles with other members of the species through the process of sexual reproduction and fertilization o Meiosis not mitosis returns the number of chromosomes back to haploid 1n 0 During meiosis there is mixing between the various alleles found on the chromosomes resulting in progeny that have an allele composition different from both parents 0 Because of the new mixes of alleles there is a greater potential that one of the progeny allele variations will now be better suited to the new environment Not every cell in a population is capable of fertilization the special type of haploid cells that can fuse together during fertilization are called gametes 0 Prior to sexual mixing organisms must create a new type of cells called gametes Haploid organisms produce gametes by mitosis Diploid organisms produce gametes by meiosis o Gametes are almost always motile swimming cells that can travel great distances to nd other compatible gametes OOOO Not every cell in a population is capable of fertilization the special type of haploid cells that can fuse together during fertilization are called gametes Sexual life cycles can have a multicellular haploid organism Mitosis involves one round of DNA replication and one round of nuclear division Meiosis involves one round of DNA replication and two rounds of nuclear division
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